The present invention relates to illumination optical apparatus for illuminating an irradiated surface with illumination light in a plurality of polarization states, exposure techniques using such an illumination optical apparatus, and methods for manufacturing an electronic device with such an exposure technique.
A lithography process for manufacturing electronic devices (including micro-devices) such as a semiconductor device or a liquid-crystal display device uses an exposure apparatus such as a batch-exposure type projection-exposure apparatus, like a stepper, or a scanning-exposure type projection-exposure apparatus, like a scanning stepper, to transfer a pattern of a mask (reticle or photomask) onto each shot region of a wafer (or glass plate). In such an exposure apparatus, exposure wavelengths have been shortened to increase the resolution. Excimer laser light sources, such as a KrF excimer layer (wavelength, 248 nm) and ArF excimer laser (wavelength, 193 nm) are nowadays being used as exposure light sources. Further, to increase the resolution, polarization illumination is used to set the polarization state of illumination to a predetermined linear polarization in accordance with the pattern of a transfer subject. An excimer laser light source emits substantially linear polarization laser light and is thus optimal for use in polarization illumination.
During an actual application, depending on the pattern of a transfer subject, the polarization direction of illumination light may be set to a random and non-polarized state. Therefore, an exposure apparatus using an excimer laser light source as an exposure light source has been proposed in which a polarization control unit includes a rotatable half-wavelength plate and a quarter-wavelength plate, which are arranged in an illumination-optical system, and an optical member for setting a non-polarized state, which is freely positionable in and out of an optical path. The rotation of the wavelength plates and positioning of the optical member in the polarization-control unit are combined to control various polarization states of illumination light that illuminate a mask. For example, refer to International Patent Publication No. 2004/051717.
In the prior art, the polarization-control unit is formed under the assumption that the laser light from the excimer laser light is in a predetermined polarization state, for example, in linear polarization in a predetermined direction. However, changes may occur in the actual laser light emitted from a laser light source such as an excimer laser light source due to time-dependent change or other reasons. Further, when a light-transmission optical system or the like extends from the excimer laser light source to the polarization-control unit, and the optical path to the polarization-control unit is long, the polarization state of the laser light may slightly change from the excimer laser light source to the polarization-control unit.
In this manner, when the polarization state of the laser light that enters the polarization-control unit changes from the designed state, the polarization state of the laser light (illumination light) emitted from the polarization-control unit may deviate from the ideal polarization state. This may lower the resolution.